In vitro studies have demonstrated that growth hormone releasing peptide (GHRP) is able to stimulate growth hormone secretion, but continuous exposure of somatotrophs to GHRP results in attenuation of response. Since GHRP likely acts at several sites, this may not occur in vivo. If it does occur, there will be no response to an intravenous bolus given 5 1/2 hr into a continuous intravenous 6 hr infusion of GHRP.